1. Field of the Invention
The present invention relates to a disc heater incorporated in a temperature control apparatus which alternately repeats heating and cooling operations in a manufacturing process of semiconductor or in a forming process of various thin films or electrode pattern with respect to glass plate of liquid crystal display, and also relates to a temperature control apparatus provided with the heater. More particularly, the present invention relates to a disc heater in which a wire-like heating element is disposed in one stroke drawing manner onto a plate surface, thereby securing thermal uniformity in a heating surface of the disc heater, and a number of excessively heated local portions is reduced. The present invention also relates to a temperature control apparatus provided with the heater.
2. Description of the Related Art
A disc heater of this kind can be applied to various processing apparatus used in film forming process of manufacture of semiconductors, etching process, photoresist application process, or light exposure process in manufacturing of crystal displays. As disclosed in Japanese Patent Laid-open Publication No. 7-183281 for example, the disc heater of this kind is used for smooth cooling control.
The disc heater disclosed in the above-described publication is a temperature adjusting heater used for controlling cooling temperature at the time of cooling process of semiconductor wafers. In a conventional low temperature processing apparatus to which this temperature adjusting heater is applied, since an electricity feeding pipe used for feeding high frequency electricity or feeding electricity to the heater is disposed in a center of a table on which an object to be processed is placed, cold temperature from a cooling jacket is less prone to be transmitted to the center region of the table. Further, since the heat from the heater is actively transmitted around a periphery of the table and thus, even when the heater is designed such that the calorific value from a heating surface of the heater becomes uniform, the entire heating surface of the heater is not heated uniformly. Therefore, there is a tendency that the center of the heater is higher in temperature than peripheral region. Thus, topology of a wire heating body of the temperature adjusting heater is set rough at a center thereof as compared with a peripheral region thereof, thereby preventing the center from being excessively heated and securing uniform temperature over the entire heating surface.
However, in a temperature control apparatus that the present inventor previously proposed in Japanese Patent Application No. 10-40765, the electricity feeding pipe as described above is not necessarily disposed in the center of the table intensively. In this case, it is preferable that an entire heating surface of the disc heater of this kind is heated uniformly.
On the other hand, in the conventional disc heater as disclosed in Japanese Patent Laid-open Publications Nos. 5-21308 and 7-183281 for example, a thick metal plate having great thermal capacity is interposed between a heating body and an object to be processed. By interposing the metal plate in such a manner, it is possible to uniformly transmit heat from the heating body to the object to be processed through the metal plate, so that it is unnecessary to pay special attention to the topology pattern of the heating body.
However, in a case of a processing apparatus which alternately repeats heating and cooling operations with respect to the object to be processed, it is preferable that after the object is heated for a predetermined time period by swiftly increasing the temperature to a preset processing temperature, the temperature is swiftly lowered to a preset cooling temperature, as shown in FIG. 16. As described above, when the thick metal plate having great thermal capacity is interposed between the heating body and the object to be processed, the thermal transmission is prone to be delayed and its control is difficult. To avoid such problems, it is ideal to bring the heating body into direct contact with the object to be processed and to heat and cool it.
Actually, the heating body is not brought into direct contact with the object to be processed, considering influence on the object to be processed, so that a surface of the heating body is covered with a metal foil which is extremely thin and has high thermal conductivity, such as aluminum foil of 0.5 mm. However, when the heating body is covered with the metal foil having great thermal conductivity, since the object to be processed is largely influenced by the topology pattern of the heating body, higher uniformity of heat of the heating body is required. Therefore, the topology pattern of the heating body becomes important.
FIGS. 17 to 19 show an example of commercially available topology pattern of a wire heating body designed so as to obtain uniform calorific value, and its locally excessively heated state. As can be understood from these drawings, in the topology pattern formed by a wire-like heating element 40, in a region of a disc heater whose center diameter is about xc2xd of the disc heater, adjacent straight lines of a large number of straight line portions 40b comprising parallel strings divided into xc2xd are sequentially connected by arc portions 40a or short straight line portions 40xe2x80x2b so that the entire pattern has continuous repeating zigzag shapes. A peripheral region of the center region is divided into two regions in a diametrical direction of the disc heater. In a region closer to the center, each diametrically adjacent pair of ends of a large number of concentrically disposed-long and short various arc portions 40a are connected by the straight line portions 40xe2x80x2b, while in a region closer to the outer periphery, each pair of diametrically adjacent ends of the arc portions 40a on an extensions in a diametrical direction of the connected portions of the ends in the above-described center region are connected by the straight line portions 40xe2x80x2b. Such a complicated topology pattern has been invented for securing thermal uniformity of the heating surface to the utmost.
In FIGS. 19A and 19B, blackened portions indicate burnt portions 40c by heat. It can be understood from distribution of the burnt portions 40c that the burnt portions are concentrated on bent portions of the wire-like heating elements, and many burnt portions 40c exist in portions where closed regions between adjacent wire-like heating elements in which heat is less prone to be released. This is caused because heating current is shortcut in the bent portions and concentrated in inner side of the bent portions. Due to the existence of the burnt portions 40c, the calorific value concentrates in such portions so that the calorific value there is remarkably increased as compared with the other portions, and the object to be processed is locally heated excessively. Further, when the excessively heating state continues, such portions are burnt to cut down wires, so that the heater can not function as a heater.
If the topology pattern is studied in detail, wire-like heating elements disposed in the outermost peripheral region are wider and a distance between the adjacent wires is narrower than the wire-like heating elements in other regions. This is because the heating density of the center of the heater is made rough so that excessive heating in the center can be avoided and the object to be processed can be processed with uniform heat, as in the temperature adjusting heater disclosed in Japanese Patent Laid-open Publication No. 7-183281. However, as described above, according to the latest processing apparatus, high frequency electricity is not always supplied to the center of the heater, or a feeding pipe used for feeding electricity to the heater or static electricity chuck is not always disposed in the center of the heater. Further, when the object to be processed is directly heated, it is required that the entire heating surface of the heater produces heat uniformly.
The present invention has been accomplished to solve all of these problems, and it is a main object of the present invention to provide a disc heater in which a thin plate surface produces heat uniformly over its entire heating surface, and which has ideal topology pattern whose local excessively heated portion is reduced to the utmost, and to provide a temperature control capable of uniformly heating and cooling an object to be processed.
These objects are effectively achieved by the following first to thirteenth aspects present invention.
According to the first aspect of the present invention, a disc heater is applied to a temperature control apparatus which controls temperature of an object to be processed on at least one surface thereof, in which a wire-like heating element is laid on a plate surface in a predetermined pattern and power feeding portions are disposed at an end of the wire-like heating element, wherein the pattern formed by the wire-like heating element includes a large number of arc portions disposed on a large number of concentric circles, and a surface area of the arc portions is 70% or greater of a surface area of the entire pattern.
In the pattern formed by the wire-like heating element, folded portions, which are folded back at acute angles, are prone to be excessively heated. Thereupon, in the present invention, 70% or more of the pattern of the wire-like heating element is constituted by the large number of arc portions disposed on the large number of concentric circles. Therefore, the local excessively heated portions are reduced, so that burning and disconnection due to such excessive heating can be avoided, thus improving the durability. Further, since the arc portions on circumferences of adjacent concentric circles are connected to each other by slight straight lines while being appropriately dispersed on the same circumferences, it is easy to uniform the heat. Further, it is preferable that the portions folded at acute angles are connected with small arcs so as to reduce the burning. Or when a plurality of slits are formed along the folded shapes in the folded portions, electric current uniformly flows through a portion of the wire-like heating element sandwiching the slits, so that the local excessively heated portions are not generated and burning is not generated.
According to a second aspect of the present invention, the surface area of the arc portions with respect to the surface area of the entire pattern is preferably in a range of 85 to 95% in view of thermal uniformity.
According to a third aspect of the present invention, the pattern formed by the wire-like heating element further includes connecting portions sequentially connecting one end of each of the arc portions disposed concentrically with one end of each of the arc portions toward a center. With this connection, the connecting portions can be set short to the utmost, so that the folded portions can be formed about at 90xc2x0 which is the limit folding angle not to be excessively heated. Therefore, the excessively heated portions can be reduced.
According to a fourth aspect of the present invention, the connecting portions are preferably disposed so as to be dispersed in different diametric regions on the concentric circles. However, the connecting portions may not only be disposed such as to be dispersed in different diametric region on the concentric circles, but also be disposed in parallel to the same diametric regions on the concentric circles. In general, it is preferable that the connecting portions are dispersed in the different diametric regions on the concentric circles because a connecting portion is prone to be heated excessively. However, even when they are disposed in parallel to the same diametric regions on the concentric circles, as far as the feature of the first aspect of the present invention is satisfied, there is no disadvantage as compared with a conventional topology pattern of this kind.
According to a fifth aspect of the present invention, the pattern of the third aspect may be combined with arc portions on concentric circles having another concentric center which is different from that of the concentric circles according to the third aspect. With this structure, especially in the pattern of the center, the portions folded at acute angles can be reduced, and lengths of the wire-like heating elements in each pattern connected in parallel can be uniformed.
According to a sixth aspect of the present invention, a surface area of each wire-like heating element per unit length is substantially equal in its longitudinal direction, and the wire-like heating element constituting the pattern is disposed at the same intervals from one another. That is, the calorific value of the wire-like heating element becomes uniform in the longitudinal direction, and the distances between the wire-like heating elements are the same, so that the thermal uniformity on the heating surface of the heater can be secured.
According to a seventh aspect of the present invention, the wire-like heating elements are in plural and connected to the power feeding portions in parallel. By connecting the plurality of wire-like heating elements to the power feeding portion in parallel, influence of burning and damage due to excessive heating or the other reason is suppressed to the minimum.
According to an eighth aspect of the present invention, the entire surface area of the wire-like heating element is 45% or greater than an area of a region of the plate disc where the wire-like heating element is disposed. By setting the entire surface area of the wire-like heating element at 45% or greater than a region in which the wire-like heating element of the disc plate is disposed, the object to be processed can be sufficiently heated, and the thermal uniformity is easily secured.
According to a ninth aspect of the present invention, the wire-like heating element is formed on a disc insulative resin film body in a predetermined pattern via a metal thin film, a power-feeding-portion-forming region comprising an insulative resin film is integrally extended from a portion of a peripheral edge of the disc insulative resin film body with predetermined width and length, the power feeding portion is formed over substantially an entire surface of the power-feeding-portion-forming region, an end edge of the power feeding portion at a side of the wire-like heating element is formed so as to extend to an inner side of the insulative resin film body beyond its peripheral edge, and a slit-like power-feeding-portion-non-forming region extending along a current path is formed at an intermediate portion of the end edge.
A disc heater having such a structure is used such that the heater is fixed on a thin disc made of aluminum for example via a welding sheet by welding, but at the time of welding, the heater is positioned and temporarily fixed on the thin disc or external force is applied to the insulative film after welding in many cases. If the end edge of the power feeding portion at the side of the wire-like heating element formed in the power-feeding-portion-forming region with a predetermined width in the circumferential direction is disposed outer side of the outer periphery of the disc insulative resin film body, and the wire-like heating element is connected to a portion of the end edge of the power feeding portion with an acute angle, when any external force is applied to the connected portion, it is prone to be cut by the outer peripheral edge of the aluminum thin disc, and the heater function is lost by a break.
Thereupon, in the present invention, the end edge of the power feeding portion at the side of the wire-like heating element is formed so as to extend to the inner side of the insulative resin film body beyond its peripheral edge, thereby preventing the break of the power feeding portion.
Further, in order to weld the disc heater to the aluminum thin disc via a welding sheet, they are welded under high temperature of about 200 to 300xc2x0 C. On the other hand, since constituting materials of the insulative resin film, the metal thin film such as stainless and the power feeding portion have different coefficients of thermal linear expansion, a portion of the power feeding portion formed over substantially the entire region of the power-feeding-portion-forming region having predetermined width and length floats up at the time of welding because of the difference in coefficient of thermal linear expansion. Therefore, wrinkle is generated, and not only the outer appearance but also functions are influenced.
In the present invention, the wrinkle is prevented by forming the slit-like power-feeding-portion-non-forming region extending along the current path in the intermediate portion of the end edge of the power feeding portion at the side of the wire-like heating element.
According to a tenth aspect of the present invention, the disc heater has around its outer periphery one or more auxiliary heater portions in which the wire-like heating element different from the heater for uniforming thermal distribution of the disc heater is laid.
For example, the auxiliary heater portion is formed into a ring-shape over the entire periphery of the disc heater. In the disc heater. Due to differences in calorific value and heat releasing value between the center portion and the peripheral portion of the disc heater, temperature gradient occurs such that the temperature of the center portion rises and the temperature of the periphery is lowered. However, by forming the auxiliary heater portion around the entire periphery of the disc heater, the temperature variation between the center portion which essentially heats and cools the object to be processed and the peripheral portion of the disc heater is reduced, so that the thermal uniformity over the entire surface of the disc heater is further enhanced.
According to an eleventh aspect of the present invention, further to the tenth aspect, the auxiliary heater portions are formed such that a gap is remained on a portion of the entire outer periphery of the disc heater, and the power feeding portion of the disc heater is connected to an end of the wire-like heating element of the disc heater through the gap of the auxiliary heater portion. Here, the gap means a region in which the wire-like heating element is not laid.
By passing the power feeding portion of the disc heater through the gap, it is possible to feed electricity to the disc heater which is surrounded by the auxiliary heaters. Therefore, it is unnecessary to lay a wire-like body for feeding power in the lower portion of the heater, and the thermal uniformity is further enhanced. Further, since the disc heater, the auxiliary heater portions and the power feeding portions can be formed on the same plane, the front and back surfaces of the disc heater can be formed into smooth flat surfaces. It is preferable that the power feeding portions of the disc heater and the auxiliary heater portions are located closely to each other because the feeding wires can be disposed in one place.
Alternatively, according to a twelfth aspect of the invention, the auxiliary heater portion may be formed over substantially an entire periphery of the disc heater, the power feeding portion of the disc heater is disposed on either front or back side of the auxiliary heater portion via an insulative layer, and is connected to one end of the wire-like heating element of the disc heater. In the eleventh aspect of the present invention, since the gap in which the wire-like heating element is not formed is provided in the auxiliary heater portions, it can not be denied that the thermal uniformity may be slightly deteriorated in the gap portion. However, in the twelfth aspect of the present invention, the power feeding portion of the disc heater can be disposed on the outer peripheral portion without forming the gap in the auxiliary heater portion, so that higher thermal uniformity can be achieved. Since the power feeding portion is not heated even though it is energized, even though the power feeding portion is disposed on either front and back side, the heating of the auxiliary heater portion is not influenced.
According to a thirteenth aspect of the present invention, there is provided a temperature control apparatus in which a disc heater on which a wire-like heating element is laid in a predetermined pattern is disposed on at least one surface for controlling a temperature of an object to be processed on the surface, wherein the pattern formed by the wire-like heating element of the disc heater include a large number of arc portions disposed on a large number of concentric circles, and a surface area of the arc portions is 70% or greater of a surface area of the entire pattern, and a heating/cooling portion by heating/cooling fluid is provided on a front and/or back surface of the disc heater.
In the temperature control apparatus, by energizing the wire-like heating element of the disc heater, the wire-like heating element is heated and the object to be processed placed on its surface is heated. At that time, since the wire-like heating element is laid on the disc heater in the above described pattern, so that the entire surface is uniformly heated, the entire object to be processed is uniformly heated. When the electric supply to the wire-like heating element is stopped, and the cooling fluid is introduced to the heating/cooling portion, the object to be processed placed on the surface is swiftly cooled. When the temperature during the cooling process must be controlled precisely, it is also possible to finely adjust the cooling temperature by energizing the wire-like heating element of the disc heater at the time of cooling operation of the heating/cooling portion. Further, it is also possible to finely adjust the heating operation by the disc heater by introducing the heating fluid to the heating/cooling portion. The heating/cooling portion can be provided with a valve for selectively introducing the heating fluid and the cooling fluid, so that the heating/cooling portion can be provided with both heating and cooling functions or either one of the heating and cooling functions.